High temperature resistant super alloys based on nickel or cobalt have been developed for use in turbine construction. Especially the material of which the blades are made, is exposed to high loads. The material of the blades must not only withstand the high temperatures (above 950.degree. C.) in the turbine, rather, it must also have a high resistance against creeping. In order to assure a high creeping resistance, especially the blade material is grown of super alloys having a macro-crystalline and partially columnar structure by using respective casting and crystallization techniques. During such growing grain boundary precipitants arise of easily oxidizing alloying additives, such as vanadium or titanium, which is disadvantageous to the corrosion resistance. As a result, the surface characteristics, such as oxidation resistance and corrosion resistance, as well as thermal fatigue resistance, deteriorate disadvantageously. Thus, coatings have been developed, such as the MCrAlX, Y-family have been developed (Metal, chromium, aluminum, X=rare earths, Y=yttrium), which improve the surface characteristics due to their high proportion of chromium and aluminum, which, on their part, form stable oxides during the operation of the turbine and which increase the bonding of the oxide layer on the coating surface due to the rare earth metal. Disadvantageous effects are caused by diffusion processes due to the different concentrations on both sides of the boundary layer between the coating surface and the coating, which lead to diffusion pores in the zone near the boundary layer so that the protective coating flakes off when exposed to thermal stress at locations having a high diffusion pore density. Furthermore, the MCrAlX, Y-layers have a tendency to thermal fatigue because between the base metal alloy and the MCrAlYX-layer there is a disproportion in the heat expansion characteristics and the MCrAlX, Y-layers are very ductile compared to the base metal.
Another technically known solution is the formation of chromium and/or aluminum enriched diffusion layers on the surface of the base metal by powder pack cementing and/or gas diffusion coating. Such coatings form oxidation resistant intermetallic phases with the base metal. Due to the higher hardness of these layers with the intermetallic phases, the fatigue strength relative to alternating stress of the structural components is disadvantageously reduced to 30% compared to the fatigue strength without such protective layer. A high micro-crack danger exists for the structural component because the heat expansion characteristic is not adapted to that of the base metal. Such danger increases with an increasing coating thickness. Thus, the coating thickness must be reduced disadvantageously to less than 100.mu.m.
In known coatings, the oxidation and corrosion sensitive components of the base metal, such as vanadium and titanium, are avoided, and stable oxide formers, such as aluminum up to, for example, 20%, and chromium up to, for example, 40% are added to the alloy. In this context the formulation of the composition of the coating becomes evermore extensive and complicated having regard to the cobalt based or nickel based super alloy to be coated in order to overcome bonding problems or to minimize diffusion processes or to build-up protective stable oxides on the surface.